The present invention relates to a new and improved construction of apparatus for the dosed dispensing of a liquid by means of an injection device, typically a syringe, which apparatus is of the type generally comprising a motor-driven spindle mechanism including a spindle shaft, a cylinder, and a piston or piston arrangement, the piston or piston arrangement being mounted to be axially displaceable with one end thereof within the cylinder and connected at its other end with the spindle shaft.
In order to inject liquids, such as for instance X-ray contrast agents into the blood vessels of living bodies or organisms, there is already known to the art an injection device essentially composed of an electric motor having a gearing drive or transmission, a spindle mechanism and a magnetic coupling. By means of switching disks appropriately arranged within the apparatus housing it is possible to operate a traction cable or the like connected with the drive spindle. The switching disks are used for pre-selecting the volume of the liquid to be injected, for monitoring the volume of such liquid as well as for providing electrical contact with further external devices. These switching disks are operated by operating knobs arranged at the housing of the apparatus. Further details of such prior art dispensing apparatus are contained in "Bulletin des schweizerischen elektronischen Vereins," Volume 1, February 1969, Nr. 3, Pages 103-107.